Chokes, i.e., fluid flow regulating devices, are used in flow lines leading from wells such as oil and/or gas wells in the earth. Some of these well flow line chokes are positive chokes (fixed flow) and others are adjustable (variable flow rate). A variable flow rate choke has a movable means for varying the amount of restriction on well fluids flowing through the choke. Normally, the movable means in the choke body is designed to mate with an insert which is fixed in the body of the choke to cause the restricting effect on the fluids. This insert acts like a valve seat, and the solid valve stem may be moved axially for greater or lesser choking of the fluid flow. Such a well flow line choke is well described in Wolcott et al., U.S. Pat. No. 4,712,579.
A number of effective and successful flow line chokes are commercially available, notably from Cameron Willis, Best, OCT, Grayloc, Thornhill-Craver, Master-Flo, and BST Lift Systems. These chokes do an excellent job of regulating the flow of oil and gas from the wellhead, controlling the rate of production and the rate of introduction of hydrocarbons into the sales stream. However, as the well becomes depleted, wellhead pressure drops, and eventually no flow regulation is required since the well operates full open and may even require a compressor to introduce the hydrocarbons into the sales stream. None of the chokes known heretofore can enhance the flow of oil and gas through the fluid flow line as the well becomes depleted and wellhead pressure decreases to a low pressure.
Thus, there remains a need for a well flow line choke which can enhance oil and gas recovery from a well at low wellhead pressure.